U.S. patent number 7,719,343 [Application Number 10/658,154] was granted by the patent office on 2010-05-18 for low noise charge pump method and apparatus.
This patent grant is currently assigned to Peregrine Semiconductor Corporation. Invention is credited to Mark L. Burgener, James S. Cable, Dylan Kelly.
United States Patent |
7,719,343 |
Burgener , et al. |
May 18, 2010 |
Low noise charge pump method and apparatus
Abstract
A charge pump method and apparatus is described having various
aspects. Noise injection from a charge pump to other circuits may
be reduced by limiting both positive and negative clock transition
rates, as well as by limiting drive currents within clock generator
driver circuits, and also by increasing a control node AC impedance
of certain transfer capacitor coupling switches. A single-phase
clock may be used to control as many as all active switches within
a charge pump, and capacitive coupling may simplify biasing and
timing for clock signals controlling transfer capacitor coupling
switches. Any combination of such aspects of the method or
apparatus may be employed to quiet and/or simplify charge pump
designs over a wide range of charge pump architectures.
Inventors: |
Burgener; Mark L. (San Diego,
CA), Kelly; Dylan (San Diego, CA), Cable; James S.
(San Diego, CA) |
Assignee: |
Peregrine Semiconductor
Corporation (San Diego, CA)
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Family
ID: |
34226728 |
Appl.
No.: |
10/658,154 |
Filed: |
September 8, 2003 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050052220 A1 |
Mar 10, 2005 |
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Current U.S.
Class: |
327/536; 363/60;
327/537 |
Current CPC
Class: |
H02M
3/07 (20130101); H03K 3/0315 (20130101); H03K
3/013 (20130101); H02M 3/073 (20130101) |
Current International
Class: |
H02M
3/18 (20060101); G05F 3/16 (20060101); H03B
5/00 (20060101) |
Field of
Search: |
;327/170,180,309,551,536-537 ;363/59-60 ;307/110
;331/57,143,150,183 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0385641 |
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Sep 1990 |
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EP |
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0 938 094 |
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Jan 1999 |
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EP |
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09-161472 |
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Jun 1997 |
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JP |
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11-252900 |
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Sep 1999 |
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JP |
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WO 95/23460 |
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Aug 1995 |
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WO |
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Other References
Maxim Integrated Products, "Charge Pumps Shine in Portable
Designs", published Mar. 15, 2001, pp. 1-13. cited by other .
Texas Instruments, "TPS60204, TPS60205, Regulated 3.3-V, 100-mA
Low-Ripple Charge Pump, Low Power DC/DC Converters", published Feb.
2001, Revised Sep. 2001, pp. 1-18. cited by other .
Sam Nork, "New Charge Pumps Offer Low Input and Output Noise"
Linear Technology Corporation, Design Notes, Design Note 243,
published Nov. 2000, pp. 1-2. cited by other .
Linear Technology, "LTC1550L/LTC1551L: Low Noise Charge Pump
Inverters in MS8 Shrink Cell Phone Designs", published Dec. 1998,
pp. 1-2. cited by other .
Lance Lascari, "Accurate Phase Noise Prediction in PLL
Synthesizers", Applied Microwave & Wireless, published May
2000, pp. 90,92,94 and 96. cited by other .
Imbernon, Lisa, Communication from the European Patent Office dated
Apr. 6, 2009, 3 pages. cited by other .
Yasuike, Kazuki, English translation of an Office Action of related
appln. No. 2006-525525 received from the Japanese Patent Office
dated Aug. 25, 2009, 3 pgs. cited by other .
Tran, Pablo N., Office Action received from the USPTO dated Oct.
29, 2009 for related U.S. Appl. No. 11/501,125, 19 pages. cited by
other .
Ebner von Eschenbach, Jennifer, Communication and Supplementary
Search Report received from the EPO dated Nov. 27, 2009 for related
U.S. Appl. No. 05763216.8, 10 pages. cited by other.
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Primary Examiner: Donovan; Lincoln
Assistant Examiner: Englund; Terry L
Attorney, Agent or Firm: Jaquez & Associates Jaquez,
Esq.; Martin J. Boling, Esq.; William
Claims
What is claimed is:
1. Charge pump apparatus for generating an output voltage supply
within a circuit, comprising: a) a transfer capacitor; b) a
plurality of transfer capacitor coupling switches, each switchable
between a conducting state and a nonconducting state under control
of at least one charge pump clock output; and c) a charge pump
clock generating circuit including a ring oscillator comprising an
odd number of not more than three inverting driver sections
cascaded sequentially in a ring such that each driver section has
an output coupled to a next driver section input, wherein a first
driver section is next after a last driver section and one of the
driver section outputs constitutes a particular charge pump clock
output controlling at least one of the transfer capacitor coupling
switches, and wherein each driver section includes i) circuitry
configured as an active current limit to limit a rate of rise of
voltage at the driver section output, and ii) circuitry configured
as an active current limit to limit a rate of fall of voltage at
the driver section output; d) wherein the plurality of transfer
capacitor coupling switches are coupled to the transfer capacitor,
and are controlled so as to couple the transfer capacitor to a
voltage source during periodic first times, and to couple the
transfer capacitor to the output voltage supply during periodic
second times that are not concurrent with the first times, further
comprising capacitive coupling circuitry configured to couple the
particular charge pump clock output as a signal to each of the
transfer capacitor coupling switches without increasing a rate of
voltage rise or fall of the signal.
2. Charge pump apparatus for generating an output voltage supply
within a circuit, comprising: a) a transfer capacitor; b) a
plurality of transfer capacitor coupling switches, each switchable
between a conducting state and a nonconducting state under control
of at least one charge pump clock output; and c) a charge pump
clock generating circuit including a ring oscillator comprising an
odd number of not more than three inverting driver sections
cascaded sequentially in a ring such that each driver section has
an output coupled to a next driver section input, wherein a first
driver section is next after a last driver section and one of the
driver section outputs constitutes a particular charge pump clock
output controlling at least one of the transfer capacitor coupling
switches, and wherein each driver section includes i) circuitry
configured as an active current limit to limit a rate of rise of
voltage at the driver section output, and ii) circuitry configured
as an active current limit to limit a rate of fall of voltage at
the driver section output; d) wherein the plurality of transfer
capacitor coupling switches are coupled to the transfer capacitor,
and are controlled so as to couple the transfer capacitor to a
voltage source during periodic first times, and to couple the
transfer capacitor to the output voltage supply during periodic
second times that are not concurrent with the first times, further
comprising a capacitive coupling circuit configured to couple the
particular charge pump clock output as a signal to the at least one
transfer capacitor coupling switch without increasing a rate of
voltage rise or fall of the signal.
3. Charge pump apparatus for generating an output voltage supply
within a circuit, comprising: a) a transfer capacitor; b) a
plurality of transfer capacitor coupling switches, each switchable
between a conducting state and a nonconducting state under control
of at least one charge pump clock output; and c) a charge pump
clock generating circuit including a ring oscillator comprising an
odd number of not more than three inverting driver sections
cascaded sequentially in a ring such that each driver section has
an output coupled to a next driver section input, wherein a first
driver section is next after a last driver section and one of the
driver section outputs constitutes a particular charge pump clock
output controlling at least one of the transfer capacitor coupling
switches, and wherein each driver section includes i) circuitry
configured as an active current limit to limit a rate of rise of
voltage at the driver section output, and ii) circuitry configured
as an active current limit to limit a rate of fall of voltage at
the driver section output; d) wherein the plurality of transfer
capacitor coupling switches are coupled to the transfer capacitor,
and are controlled so as to couple the transfer capacitor to a
voltage source during periodic first times, and to couple the
transfer capacitor to the output voltage supply during periodic
second times that are not concurrent with the first times, further
comprising a capacitive coupling circuit configured to couple one
of the at least one charge pump clock outputs to a control node of
one of the plurality of transfer capacitor coupling switches.
4. The apparatus of claim 3, wherein the capacitive coupling
circuit does not conduct substantial charge to the transfer
capacitor.
5. Charge pump apparatus for generating an output voltage supply
within a circuit, comprising: a) a transfer capacitor; b) a
plurality of transfer capacitor coupling switches, each switchable
between a conducting state and a nonconducting state under control
of at least one charge pump clock output; and c) a charge pump
clock generating circuit including a ring oscillator comprising an
odd number of not more than three inverting driver sections
cascaded sequentially in a ring such that each driver section has
an output coupled to a next driver section input, wherein a first
driver section is next after a last driver section and one of the
driver section outputs constitutes a particular charge pump clock
output controlling at least one of the transfer capacitor coupling
switches, and wherein each driver section includes i) circuitry
configured as an active current limit to limit a rate of rise of
voltage at the driver section output, and ii) circuitry configured
as an active current limit to limit a rate of fall of voltage at
the driver section output; d) wherein the plurality of transfer
capacitor coupling switches are coupled to the transfer capacitor,
and are controlled so as to couple the transfer capacitor to a
voltage source during periodic first times, and to couple the
transfer capacitor to the output voltage supply during periodic
second times that are not concurrent with the first times, further
comprising corresponding capacitive coupling circuits to couple a
control node of each of the plurality of transfer capacitor
coupling switches to the particular charge pump clock output.
6. The apparatus of claim 5, wherein none of the corresponding
capacitive coupling circuits is configured to conduct substantial
charge to the transfer capacitor.
7. Charge pump apparatus for generating an output voltage supply
within a circuit, comprising: a) a transfer capacitor; b) a
plurality of transfer capacitor coupling switches, each switchable
between a conducting state and a nonconducting state under control
of at least one charge pump clock output; and c) a charge pump
clock generating circuit including a ring oscillator comprising an
odd number of not more than three inverting driver sections
cascaded sequentially in a ring such that each driver section has
an output coupled to a next driver section input, wherein a first
driver section is next after a last driver section and one of the
driver section outputs constitutes a particular charge pump clock
output controlling at least one of the transfer capacitor coupling
switches, and wherein each driver section includes i) circuitry
configured as an active current limit to limit a rate of rise of
voltage at the driver section output, and ii) circuitry configured
as an active current limit to limit a rate of fall of voltage at
the driver section output; d) wherein the plurality of transfer
capacitor coupling switches are coupled to the transfer capacitor,
and are controlled so as to couple the transfer capacitor to a
voltage source during periodic first times, and to couple the
transfer capacitor to the output voltage supply during periodic
second times that are not concurrent with the first times, further
comprising capacitively coupling substantial charge into the
transfer capacitor via the charge pump clock output.
8. Charge pump apparatus for generating an output voltage supply
within a circuit, comprising: a) a transfer capacitor; b) a
plurality of transfer capacitor coupling switches, each switchable
between a conducting state and a nonconducting state under control
of a charge pump clock output and including i) a common discharge
switch disposed between a terminal of the transfer capacitor and a
common reference connection of the output voltage supply, and
having a first control node AC impedance, and ii) an output supply
discharge switch disposed between an opposite terminal of the
transfer capacitor and a connection of the output voltage supply
opposite the common reference connection, and having a second
control node AC impedance at least twice the first control node AC
impedance; and c) a charge pump clock generating circuit including
i) circuitry configured to limit a rate of rise of the charge pump
clock output, and ii) circuitry configured to limit a rate of fall
of the charge pump clock output; d) wherein the transfer capacitor
coupling switches are coupled to the transfer capacitor, and are
controlled so as to couple the transfer capacitor to a voltage
source during periodic first times, and to couple the transfer
capacitor to the output voltage supply during periodic second times
that are not concurrent with the first times.
9. Charge pump apparatus within a monolithic integrated circuit for
generating an output voltage supply, comprising: a) a transfer
capacitor coupled alternately between source connections and output
connections; b) a plurality of active switches, each switchable
between a conducting state and a nonconducting state under control
of at least one charge pump clock output to couple charge, which is
not substantially conducted by the charge pump clock output, from
the source connections to the output connections; c) a charge pump
clock generating circuit including an active driver circuit
configured to both source current to and sink current from the
charge pump clock output to cause a voltage waveform of the charge
pump clock output to be substantially sine-like due to i) circuitry
configured to limit source current provided by the active driver
circuit to the charge pump clock output, and ii) circuitry
configured to limit current sunk from the charge pump clock output
by the active driver circuit, further comprising one or more
capacitive coupling networks configured to couple one of the at
least one charge pump clock outputs to a control node of at least
one of the plurality of active switches, wherein the capacitive
coupling necessitates the charge pump clock output to be
substantially sine-like.
10. The apparatus of claim 9, wherein the charge pump clock
generating circuit is configured as a current starved ring
oscillator.
11. The apparatus of claim 9, wherein the source current circuitry
c) i) and the sink current circuitry c) ii) are configured to limit
source and sink currents to a substantially identical
magnitude.
12. Charge pump apparatus for generating an output voltage supply
within a monolithic integrated circuit, comprising: a) a transfer
capacitor; b) one or more source switching devices disposed in
series between the transfer capacitor and a voltage source to
convey transfer current to the transfer capacitor from the voltage
source when conducting; c) one or more output switching devices
disposed in series between the transfer capacitor and the output
voltage supply to convey transfer current from the transfer
capacitor to the output voltage supply when conducting; and d) a
charge pump clock generating circuit configured to provide a
single-phase charge pump clock output coupled capacitively, without
conveying substantial transfer current, to control nodes of each of
the source switching devices to cause conduction during charge
periods and nonconduction during discharge periods for all of the
source switching devices, the charge pump clock output further
coupled capacitively, without conveying substantial transfer
current, to control nodes of each of the output switching devices
to cause nonconduction during the charge periods and conduction
during the discharge periods for all of the output switching
devices, wherein the charge periods alternate with, and do not
overlap, the discharge periods.
13. The apparatus of claim 12, which includes a first charge pump
having at least a first example of each recited feature, further
comprising a second charge pump stage including: e) a second
transfer capacitor; f) one or more second-source switching devices
disposed in series between the second transfer capacitor and a
second voltage source; and g) one or more second-output switching
devices disposed in series between the second transfer capacitor
and a second output voltage supply; h) wherein the charge pump
clock output is coupled to all of the second-source switching
devices to cause conduction during the charge periods and
nonconduction during the discharge periods, and is coupled to all
of the second-output switching devices to cause nonconduction
during the charge periods and conduction during the discharge
periods.
14. The apparatus of claim 12, further comprising circuitry
configured to reduce voltage change rates of the charge pump clock
output during both positive and negative transitions compared to an
absence of such circuitry such that the charge pump clock output
voltage is substantially sine-like and wherein the capacitive
coupling of the charge pump clock output necessitates that the
charge pump clock output be substantially sine-like.
15. The apparatus of claim 12, wherein the charge pump clock
generating circuit (d) further comprises circuitry configured to
limit currents conducted by each amplifying driver circuit in the
charge pump clock generating circuit.
16. The apparatus of claim 15, further comprising a discrete
capacitive device coupled to an output of one of the amplifying
driver circuits to limit a rate of voltage change of the driver
circuit output.
17. The apparatus of claim 12, wherein each of the source switching
devices and each of the output switching devices is a transfer
capacitor ("TC") switching device, each such TC switching device is
either an n-channel FET or a p-channel FET, and wherein threshold
voltages of all n-channel TC switching devices are substantially
similar, and threshold voltages of all p-channel TC switching
devices are substantially similar.
18. Charge pump apparatus for generating an output voltage supply
within a circuit, comprising: a) a transfer capacitor; b) one or
more source switching devices disposed in series between the
transfer capacitor and a voltage source; c) a first output
switching device having a first device area disposed between a
first terminal of the transfer capacitor and the output voltage
supply, and a second output switching device disposed between a
common reference connection of the output voltage supply and a
second terminal of the transfer capacitor opposite the first
terminal of the transfer capacitor, having a second device area
that is greater than double the first device area; and d) a charge
pump clock generating circuit configured to provide a single-phase
charge pump clock output coupled to all of the source switching
devices to cause conduction during charge periods and nonconduction
during discharge periods for all of the source switching devices,
the charge pump clock output further coupled to all of the output
switching devices to cause nonconduction during the charge periods
and conduction during the discharge periods for all of the output
switching devices.
19. Charge pump apparatus for generating an output voltage supply
within a monolithic integrated circuit, comprising: a) a transfer
capacitor for conveying charge from a voltage source to the output
voltage supply; b) one or more source switching devices disposed in
series between the transfer capacitor and the voltage source, each
having a corresponding control node that is substantially isolated
from both the transfer capacitor and the voltage source; c) one or
more output switching devices disposed in series between the
transfer capacitor and the output voltage supply, each having a
corresponding control node that is substantially isolated from both
the transfer capacitor and the voltage source; and d) a capacitive
coupling circuit coupling a charge pump clock output to one of the
control nodes corresponding to a source switching device or to an
output switching device.
20. The apparatus of claim 19, wherein the capacitive coupling
circuit is a first capacitive coupling circuit coupling the charge
pump clock output to a source switching device control node, and
further comprising a second capacitive coupling circuit coupling
the charge pump clock output to an output switching device control
node.
21. The apparatus of claim 20, wherein each of the capacitive
coupling circuits includes biasing circuitry configured such that
an average control voltage causes a switching device to which it is
coupled to be substantially nonconductive.
22. The apparatus of claim 20, wherein all source switching devices
disposed in series between the transfer capacitor and the voltage
source, and all output switching devices disposed in series between
the transfer capacitor and the output voltage, are capacitively
coupled to the charge pump clock output.
23. A method of generating an output supply from a charge pump
incorporated within a monolithic integrated circuit by transferring
charge from a source voltage to a transfer capacitor ("TC")
alternately with transferring charge from the TC to the output
supply, wherein a TC-coupling switch ("TCCS") circuit is a
switching circuit of the charge pump configured to couple the TC to
a supply under control of a charge pump clock, the method
comprising: a) coupling the TC to the output supply during
discharge periods via a discharging TCCS circuit under control of a
first charge pump clock output; and b) actively limiting a rate of
voltage change of the first charge pump clock output during both
positive transitions and negative transitions such that a voltage
of the first charge pump clock output is substantially sine-like,
further comprising capacitively coupling the first charge pump
clock output to a control node of a TCCS circuit thereby
necessitating that the first charge pump clock output be
substantially sine-like.
24. The method of claim 23, wherein actively controlled TCCS
circuits each have an associated control node, the method further
comprising coupling the associated control node of each of the
actively controlled TCCS circuits to the first charge pump clock
output via a corresponding capacitive coupling circuit.
25. The method of claim 23, wherein a first clock generator driver
circuit is a driver circuit functionally incorporated in a first
clock generator circuit configured to generate the first charge
pump clock output, the method further comprising: c) limiting
source currents from a particular first clock generator driver
circuit by means of a first current limiting circuit; and d)
limiting sink currents into the particular first clock generator
driver circuit by means of a second current limiting circuit.
26. The method of claim 25, further comprising limiting the source
currents and the sink currents of the particular first clock
generator driver circuit to substantially identical magnitudes.
27. The method of claim 25, wherein the first current limiting
circuit comprises a current mirror device, and the second current
limiting circuit comprises a different current mirror device.
28. The method of claim 26, further comprising limiting source
currents and sink currents from all first clock generator driver
circuits.
29. The method of claim 23, further comprising generating the first
charge pump clock output by means of a current starved ring
oscillator including not more than three inverting driver sections
coupled in a ring.
30. The method of claim 23, further comprising coupling the TC to
the source voltage or to the output supply in part via a passive
TCCS circuit.
31. A method of generating an output supply within a monolithic
integrated circuit by alternately transferring charge from a
voltage source to a transfer capacitor ("TC"), and from the TC to
the output supply, the method comprising: a) coupling the TC to the
output supply during discharge periods via a TC discharging switch
under control of a single phase charge pump clock output that is
capacitively coupled to a control node of the TC discharging switch
and substantially isolated from the TC; and b) coupling the TC to
the voltage source via a TC charging switch, during charge periods
that nonoverlappingly alternate with the discharge periods, under
control of the single-phase charge pump clock output that is
capacitively coupled to a control node of the TC charging
switch.
32. A method of generating an output supply from a charge pump by
transferring charge from a source voltage to a transfer capacitor
("TC") alternately with transferring charge from the TC to the
output supply, wherein a TC-coupling switch ("TCCS") circuit is a
switching circuit of the charge pump configured to couple the TC to
a supply under control of a charge pump clock, the method
comprising: a) coupling the TC to the output supply during
discharge periods via a discharging TCCS circuit under control of a
first charge pump clock output; b) actively limiting a rate of
voltage change of the first charge pump clock output during both
positive transitions and negative transitions; c) coupling a first
terminal of the TC to a common reference connection of the output
supply via a discharge common TCCS; d) coupling a second opposite
terminal of the TC to an output supply connection opposite the
common reference connection via a discharge output TCCS; and e)
fabricating the discharge output TCCS to have a control node AC
impedance at least double a control node AC impedance of the
discharge common TCCS.
33. A method of generating an output supply by alternately
transferring charge from a source voltage to a transfer capacitor
("TC"), and from the TC to the output supply, the method
comprising: a) coupling the TC to the output supply during
discharge periods via a discharging switch circuit under control of
a first charge pump clock output; b) limiting source current
provided to each inverting driver output node of a current starved
ring oscillator having not more than three inverting driver stages
within a first charge pump clock generator circuit by means of a
corresponding source current-limiting circuit; and c) limiting sink
current drawn from each of the inverting driver output nodes by
means of a corresponding sink current-limiting circuit; wherein the
inverting driver output node of one of the not more than three
inverting driver stages of the first charge pump clock generator
circuit is the first charge pump clock output, further comprising
coupling the first charge pump clock output to a control node of
the discharging switch circuit and/or to a control node of a
charging switch via a corresponding capacitive coupling
circuit.
34. The method of claim 33, further comprising coupling the first
charge pump clock output as a signal to a control node of the
discharging switch circuit via a capacitive network that is not
configured to increase rates of voltage change of the signal.
35. The method of claim 33, wherein the number of driver stages of
the ring oscillator is not less than three.
36. The method of claim 31, wherein the TC charging switch and the
TC discharging switch comprise TC switching devices, and are either
n-channel or p-channel FETs, and wherein threshold voltages of all
n-channel TC switching devices are substantially similar, and
threshold voltages of all p-channel TC switching devices are
substantially similar.
37. The method of claim 31, wherein step a) further comprises
coupling the TC to the output supply during discharge periods via a
plurality of TC discharging switches under control of the single
phase charge pump clock output.
38. The method of claim 37, wherein step b) further comprises
coupling the TC to the voltage source via a plurality of TC
charging switches under control of the single phase charge pump
clock output.
39. The method of claim 31, further comprising: c) coupling a
second TC to a second voltage source via a second TC charging
switch under control of the charge pump clock output; and d)
coupling the second TC to a second output supply via a second TC
discharging switch under control of the charge pump clock output,
and further comprising coupling the charge pump clock output to a
control node of each TC charging switch, and to a control node of
each TC discharging switch, via corresponding capacitive coupling
circuits.
40. The method of claim 31, further comprising incorporating
circuitry to reduce voltage change rates during both positive and
negative transitions of the charge pump clock output.
41. The method of claim 31, further comprising: c) generating the
charge pump clock output in a charge pump clock generator circuit
having one or more driver circuits, and d) limiting currents output
from each driver circuit of the charge pump clock generator
circuit.
42. The method of claim 41, further comprising: e) limiting rates
of both positive and negative voltage transitions at an output node
of one of the driver circuits of the charge pump clock generator
circuit by coupling a capacitor to the output node of the driver
circuit.
43. A method of generating an output supply by alternately
transferring charge from a voltage source to a transfer capacitor
("TC"), and from the TC to the output supply, the method
comprising: a) coupling the TC to the output supply during
discharge periods via a plurality of TC discharging switches under
control of a single phase charge pump clock output; b) coupling the
TC to the voltage source via a TC charging switch, during charge
periods that nonoverlappingly alternate with the discharge periods,
under control of the single-phase charge pump clock output; c)
coupling a first TC discharging switch in series between a first
node of the TC and a common reference connection of the output
supply; d) coupling a second TC discharging switch in series
between a second node of the TC opposite the first node and a
connection of the output supply opposite the common reference
connection; and e) fabricating the second TC discharging switch to
have a control node AC impedance at least twice as large as a
control node AC impedance of the first discharging switch.
44. The method of claim 43, wherein the step b) further comprises
coupling the TC to the voltage source via a plurality of TC
charging switches under control of the single phase charge pump
clock output.
45. A method of generating an output supply within a monolithic
integrated circuit by alternately transferring charge from a
voltage source to a transfer capacitor ("TC"), and from the TC to
the output supply, the method comprising: a) coupling the TC to the
output supply during discharge periods via a first actively
controllable TC discharging switch under control of a single phase
charge pump clock output that is capacitively coupled to a control
node of the first actively controllable TC discharging switch and
substantially isolated from the TC; b) coupling the TC to the
voltage source via a first actively controllable TC charging
switch, during charge periods that nonoverlappingly alternate with
the discharge periods, under control of the single-phase charge
pump clock output that is capacitively coupled to a control node of
the first actively controllable TC charging switch; c) coupling a
second TC to a second voltage source via a second actively
controllable TC charging switch under control of the charge pump
clock output; and d) coupling the second TC to a second output
supply via a second actively controllable TC discharging switch
under control of the charge pump clock output; further comprising
coupling the charge pump clock output to a control node of each
actively controllable TC charging switch, and to each actively
controllable TC discharging switch, via corresponding capacitive
coupling circuits.
46. A method of generating an output supply within a monolithic
integrated circuit by alternately transferring charge for the
output supply from a source voltage to a transfer capacitor ("TC"),
and from the TC to the output supply, the method comprising: a)
coupling a first charge pump clock output to a control node of a TC
charging switch via a first capacitive coupling network that does
not conduct a significant portion of the charge for the output; b)
coupling the TC to the source voltage during charge periods via the
TC charging switch under control of the first charge pump clock
output; c) coupling a second charge pump clock output to a control
node of a TC discharging switch via a second capacitive coupling
network that does not conduct a significant portion of the charge
for the output; and d) coupling the TC to the output supply via the
TC discharging switch during discharge periods nonconcurrently
alternating with the charge periods under control of the second
charge pump clock output.
47. The method of claim 46, wherein the second charge pump clock
output is the first charge pump clock output.
48. The method of claim 47, further comprising biasing each of the
capacitive coupling networks such that the TC charging or
discharging switch to which it is coupled is nonconductive when the
first charge pump clock output is at an average value of its
time-varying voltage.
49. The method of claim 48, further comprising coupling the TC to
the source voltage during the charge periods via an additional
second TC charging switch having a control node capacitively
coupled to a corresponding second charge pump output.
50. The method of claim 49, wherein the TC discharging switch is a
first TC discharging switch and is coupled between a first node of
the TC and a connection of the output supply opposite a common
reference, the method further comprising coupling an opposite
second node of the TC to the common reference of the output supply
during the discharge periods via a second TC discharging switch
having a control node AC impedance no more than half as large as a
control node AC impedance of the first TC discharging switch.
51. The method of claim 48, further comprising coupling the TC to
the output supply during the discharge periods via an additional
second TC discharging switch having a control node capacitively
coupled to a corresponding second charge pump output.
52. The method of claim 46, further comprising capacitively
coupling a control node of each actively controllable TC coupling
switch, corresponding to the TC charging switch and the TC
discharging switch, that is incorporated within a charge pump to a
corresponding charge pump clock output.
53. The method of claim 52, wherein all of the corresponding charge
pump clock outputs are a common single-phase output.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to electronic power supplies, and
more specifically to capacitive energy transfer DC-to-DC converters
(DC/DC converters), such as charge pumps.
2. Related Art
DC/DC converter power supply circuits provide a DC output voltage
based upon a DC source voltage. The output is typically at a
different voltage than the input. As the term is used herein, DC/DC
converters do not encompass voltage reduction regulator circuits
that use a linear pass device, but rather involve energy transfer
from input to output through an energy storage device, such as a
capacitor or an inductor.
The DC/DC converters of interest herein are charge pumps, which
obtain energy for the output voltage primarily by means of
capacitive transfer from the source to the output. An inductor is
not generally the primary energy transfer device in a charge pump,
though of course hybrid devices are possible that employ inductive
energy transfer in addition to capacitive energy transfer. A charge
pump may derive an output voltage that is higher than a source
voltage, or that is inverted from a source voltage, or that is
referenced to a different voltage than the source voltage, and
indeed may do all of these things concurrently.
Charge pumps may be implemented for a wide variety of purposes.
They are well suited for integrated circuit fabrication because the
devices and elements required are compatible with most integrated
circuit fabrication techniques. For example, a charge pump may be
employed to generate a negative gate bias supply for an integrated
circuit that switches an antenna between send and receive circuitry
of a transceiver, as shown in FIG. 1. Many wireless transceivers,
such as cellular telephones, employ a single antenna for both
receiving and transmitting. While such systems are receiving, an
antenna 102 must be coupled to receive circuitry that may include,
for example, a filter 104 and a low noise amplifier 106, to provide
the received signal for further processing. However, while such
systems are transmitting, the antenna 102 must be disconnected from
the sensitive receive circuitry and coupled instead to relatively
high power transmit circuitry. The transmit circuitry may include,
for example, a power amplifier 108 and a transmit filter 110 to
process a transmit signal.
A RF switch 112 may be used to perform such antenna switching
functions. Ideally, such switches may be integrated together with
the receive and/or transmit circuitry, and in any event are
desirably very small, due to space limitations in portable
transceivers such as mobile telephones and handy talkies. In order
to achieve good performance from switching devices, such as
MOSFETs, used to implement such RF switches, many designs need a
special bias supply that extends negatively below the supply rails
of the transmit and receive circuitry, such as a -3V supply. In
view of the space and cost constraints of transceiver units such as
mobile telephones, a charge pump is particularly suitable for
generating such a bias supply, because it can be readily integrated
into a very small circuit.
The RF switch 112 conveys relatively high power signals to the
antenna 102 during transmission. However, during receive, the
signal passed by the RF switch 112 may be measured in tens of
nanovolts. Sharp noise transitions may have an extremely broad
Fourier frequency content, and thus even signals at amplitudes on
the order of millivolts may interfere unacceptably with reception
if the signals have extremely fast edges. While the filter 104 can
remove some noise, it is important that the RF switch 112 not
introduce noise, particularly noise having components near the
center frequency of the received signal. Thus, the receive/transmit
switch of FIG. 1 illustrates one of many circumstances in which a
charge pump may be desired for a circuit that nonetheless requires
extremely low noise.
Unfortunately, noise generation is one of the most common drawbacks
of charge pumps. Current spikes are typically coupled into both
input and output supplies, together with voltage ripples and
spikes. When a charge pump is integrated together with other
devices, such electronic noise may be coupled throughout the
circuitry of the integrated device by a variety of mechanisms that
are difficult to control. Thus, a need exists for charge pumps that
avoid generating excessive noise, so as to reduce charge pump noise
injection into source supplies, output supplies, and related
circuits.
The method and apparatus presented herein address this need for a
low-noise charge pump. Various aspects of the method and apparatus
described herein will be seen to provide further advantages, as
well, for the design and construction of charge pumps that are
relatively free of noise spurs.
SUMMARY
A charge pump method and apparatus for DC-to-DC conversion is set
forth by which an output is generated by alternately coupling a
transfer capacitor to an input supply and then to the output. A
charge pump clock output is generated to control a transfer
capacitor coupling switch in a charge pump circuit. The charge pump
method (or apparatus) further includes a combination of one or more
aspects of the method or apparatus, as set forth below, in order to
reduce noise or otherwise improve the design.
One aspect of the charge pump method described herein includes
generating an output supply by transferring charge from a source
voltage to a transfer capacitor ("TC") alternately with
transferring charge from the TC to the output supply. A TC-coupling
switch ("TCCS") circuit is a switch that couples the TC to a supply
under control of a charge pump clock ("CPClk"). This method
includes coupling the TC to the output supply during discharge
periods via a discharging TCCS circuit, and actively limiting a
rate of voltage change of the CPClk output during both positive and
negative transitions.
An aspect of the charge pump apparatus described herein may be
employed to generate an output voltage supply within a circuit.
This aspect includes a transfer capacitor ("TC") and a plurality of
TC coupling switches ("TCCSs"), each TCCS controlled by a charge
pump clock ("CPClk") output. The apparatus also has a CPClk
generation circuit, which includes circuitry that limits a rate of
rise of the CPClk output and circuitry that limits a rate of fall
of the CPClk output. The TCCSs are coupled to the TC, and are
controlled to couple the TC to a voltage source during periodic
first periods, and to couple the TC to the output voltage during
periodic second periods that are not concurrent with the first
periods.
Another aspect of the charge pump apparatus described herein may be
also be used for generating an output voltage supply within a
circuit. This aspect includes a transfer capacitor ("TC") coupled
alternately between source connections and output connections, and
a plurality of active switches that are each switchable under
control of a charge pump clock ("CPClk") output to conduct, or not.
This aspect includes a CPClk generating circuit that has an active
driver circuit configured to source current to, and sink current
from, a driver output node, together with circuitry to limit the
source current, and circuitry to limit the sink current, of the
active driver circuit.
Another aspect of the charge pump described herein is a method of
alternately transferring charge from a source voltage to a transfer
capacitor ("TC"), and from the TC to an output supply, to generate
an output supply. The method includes coupling the TC to the output
supply via a discharging switch under control of a charge pump
clock ("CPClk") output. The method also includes limiting source
and sink currents between a driver circuit and a corresponding
output node, within a generator circuit of the CPClk.
Yet another aspect of the charge pump method described herein
alternately transfers charge from a source voltage to a transfer
capacitor ("TC"), and from the TC to an output supply. This method
includes coupling the TC to the output supply during discharge
periods via a discharging switch circuit under control of a single
phase charge pump clock ("CPClk") output, and coupling the TC to
the voltage source via a charging switch circuit under control of
the single phase CPClk output.
A related aspect of the charge pump apparatus described herein may
be used for generating an output voltage supply. This apparatus
includes a transfer capacitor ("TC"), one or more source switching
devices in series between the TC and the source voltage, and one or
more output switching devices in series between the TC and the
output supply. A single phase output of a charge pump clock
("CPClk") generating circuit is coupled to all of the source
switching devices to cause them to conduct only during charge
periods, and is also coupled to all of the output switching devices
to cause them to conduct only during discharge periods, wherein the
charge and discharge periods alternate and do not overlap.
A further aspect of the charge pump method described herein may
generate an output supply by alternately transferring charge from a
source voltage to a transfer capacitor ("TC"), and from the TC to
the output supply. This method includes coupling a first charge
pump clock ("CPClk") output to a TC charging switch control node
via a first capacitive coupling network, and coupling the TC to the
source voltage during charge periods under control of the first
CPClk output. The method also includes coupling a second CPClk
output to a TC discharging switch control node via a second
capacitive coupling network, and coupling the TC to the output
supply during discharge periods that nonconcurrently alternate with
the charge periods, under control of the second CPClk output.
A further aspect of the charge pump apparatus described herein may
be used for generating an output voltage supply, and includes a
transfer capacitor ("TC"). This apparatus includes one or more
source switching devices, having a corresponding control node,
disposed in series between the TC and a source supply, and also
includes one or more output switching devices, having corresponding
control nodes, disposed in series between the TC and the output
supply. This apparatus also includes a capacitive coupling circuit
coupling a charge pump clock output to the control node of a source
switching device or to the control node of an output switching
device.
Yet a further method aspect of the charge pump described herein
includes steps of disposing an output hot switch between a transfer
capacitor ("TC") node and a charge pump output, and disposing an
output common switch between the opposite TC node and a common
connection of the charge pump output. This method also includes
establishing a higher control node AC impedance for the hot switch,
as compared to a control node AC impedance for the output common
switch. A related aspect provides apparatus generally corresponding
to this method.
Embodiments of the charge pump method or apparatus may employ any
combination of individual aspects of the method or apparatus, and
may be configured in a wide range of charge pump architectures and
configurations.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will be more readily
understood by reference to the following figures, in which like
reference numbers and designations indicate like elements.
FIG. 1 is a block diagram illustrating use of a RF switch.
FIG. 2 is a block diagram illustrating basic charge pump
operations.
FIG. 3 is a charge pump schematic diagram illustrating some of the
current paths in which noise may be reduced by employing aspects of
the method and apparatus described herein.
FIG. 4 is a schematic diagram of exemplary current-limited
inverters.
FIG. 5 is a schematic diagram of a current-starved oscillator for a
charge pump.
FIG. 6 is a schematic diagram of a charge pump in which the active
switches are coupled to control signals by means of capacitive
coupling.
FIG. 7 is a schematic diagram of a charge pump employing passive
switches.
FIG. 8 is a schematic diagram of charge pump switches having a
control node capacitively coupled to a charge pump clock
output.
FIG. 9 is a block diagram illustrating alternative charge pump
configurations.
FIG. 10 is a block schematic diagram illustrating techniques for
using charge pumps to produce arbitrary output voltages.
DETAILED DESCRIPTION
Overview
Charge Pump Configurations
FIG. 2 illustrates some basic charge pump operations. Filtering
capacitors, typically present on each input and output supply, are
omitted from FIG. 2 to avoid confusion with an energy transfer
capacitor C.sub.T 202. When S1 204 and S2 206 are closed, C.sub.T
202 is connected to the source DC supply connections V.sub.S+ 208
and V.sub.S- 210, and thus C.sub.T 202 is charged to the voltage
V.sub.S, having a value [(Vs+)-(Vs-)]. S1 204 and S2 206 are then
opened, permitting C.sub.T 202 to float. Next, S3 212 and S4 214
are closed, causing the floating transfer capacitor C.sub.T 202 to
"fly" to the output supply (for which reason such capacitors are
also called fly capacitors). The charged C.sub.T is thus connected
to output supply connections Vo1+ 216 and Vo1- 218 (output Vo1).
Presuming that the voltage of output Vo1 is smaller than the
voltage stored on C.sub.T 202, C.sub.T 202 discharges, transferring
energy to Vo1, which may be an output supply.
Many different output configurations are possible using just these
four switches S1 204, S2 206, S3 212 and S4 214, together with the
transfer capacitor C.sub.T 202. A first example is a voltage
doubling configuration, wherein Vo1- 218 is connected to V.sub.S+
208, causing Vo1+ 216 to achieve a voltage roughly twice that of
V.sub.S+ 208 (both with respect to V.sub.S- 210, neglecting
losses). A second example is a voltage inverting configuration, in
which Vo1+ 216 is connected to V.sub.S- 210, such that Vo1- will
reach approximately -V.sub.S (with respect to V.sub.S- 210). A
third example is a supply isolating configuration, in which neither
Vo1+ 216 nor Vo1- 218 is tied through a fixed voltage connection to
a source voltage connection. Rather, the input lines may be
isolated from the output insofar as is permitted by the isolation
capability of the switches S1 204 and S3 212, and of the switches
S2 206 and S4 214.
The skilled person will understand certain features without a need
for explicit details. For example, because the transfer capacitor
C.sub.T 202 must be disconnected from the output while connecting
to the input, maintaining a reasonably constant voltage on the
output generally requires a storage device. Such storage device
typically comprises a filter capacitor, which is not shown in FIG.
2. As another example, current and voltage for the output may vary
depending upon many factors. The skilled person may make allowance
for such factors to anticipate a voltage of the output, or may
choose to regulate the voltage of the output. Such regulation is
not shown, but may, for example, comprise controlling the frequency
of "pump" cycles during which C.sub.T 202 is first charged to
V.sub.S and then discharged to voltage Vo1. Regulation may also
comprise controlling a value of the voltage source for the charge
pump, as described with respect to FIG. 10 below.
Additional output connection switches, such as S5 220 and S6 222,
may enable a charge pump to provide other voltages, multiplexing
the use of a single transfer or fly capacitor C.sub.T 202. For
example, charge and discharge cycles may alternate without
overlapping. C.sub.T may be charged to V.sub.S during each charge
cycle. However, during one discharge cycle, C.sub.T may be
discharged to Vo2 (Vo2+ 224 to Vo2- 226), while during another
discharge cycle C.sub.T is discharged to Vo1. In this manner, three
voltages of roughly equal value may be created--V.sub.S, Vo1 and
Vo2. The connections made between these voltages determines whether
the charge pump circuit functions as a voltage tripler, or as a
double-voltage inverter, an isolated 2*V.sub.S supply, two isolated
outputs, etc. These principles may be extended to further output
combinations.
In typical implementations, each of the switches S1 204, S2 206, S3
212 and S4 214 (as well as other switches if used, such as S5 220
and S6 222) may comprise an appropriate transistor, such as a
MOSFET. However, in many circumstances it is possible to substitute
a simple diode for a switch, when the voltage and current flow
requirements of the particular configuration of a specific charge
pump circuit permit.
The basic charge pump architecture illustrated in FIG. 2 may also
be replicated for operation in a "push-pull" fashion. For this
purpose, a second C.sub.T may be connected to Vs while the first
C.sub.T is connected to Vo1, and then such second C.sub.T may be
discharged to Vo1 the first C.sub.T is connected to V.sub.S. Such
techniques may provide more constant current capacity to the output
supply, and may aid in reducing output voltage ripple. Thus, charge
pump DC/DC converters may be designed in a wide range of
configurations to provide many different outputs from a single DC
supply.
Charge Pump Noise
As noted above, noise is one of the most common problems associated
with charge pumps. FIG. 3 illustrates an exemplary charge pump
architecture, showing some of the paths in which noise currents may
typically occur. The charge pump of FIG. 3 includes a transfer
capacitor C.sub.T 202, together with source supply connections Vs+
208 and Vs- 210, which are substantially as shown in FIG. 2, and
accordingly are identically numbered. FIG. 3 also includes output
supply connections Vo+ 316 and Vo- 318. The fly capacitor coupling
switches, which couple C.sub.T 202 to the source supply Vs or to
the output supply Vo, are shown as MOSFET devices controlled by a
signal applied to a control node (the device gate). The fly
capacitor coupling switches include a P-channel switch 304 under
control of a first clock output 354, a P-channel switch 306 under
control of a second clock output 356, an N-channel switch 314 under
control of a third clock output 362, and an N-channel switch 312
under control of a fourth clock output 364. The four charge pump
clock outputs (354, 356, 362, and 364) are generated in a charge
pump clock generator circuit 350. A filter capacitor 330 for the
output supply Vo, as well as a current load 332 on Vo, are also
shown.
Four ammeters are represented to illustrate paths in which noise
currents may occur. From these paths, noise may be unintentionally
coupled other circuits associated with the charge pump. For
example, voltage noise may be coupled into other circuits through
common supply connections, or via parasitic capacitive coupling,
while current noise may be injected into other circuits through
inductive coupling, or via a shared impedance. A source loading
ammeter 342 is disposed between the source supply Vs+ 208 and the
switch 304, and an output charging ammeter 344 is disposed between
the switch 312 and the output filter capacitor 330. Clock generator
ammeters are disposed between the clock generator 350 and its
supply source, with ammeter 346 between Vs+ 208 and clock generator
350, and ammeter 348 between the clock generator 350 and Vs- 210.
The explanation of charge pump noise currents, which is set forth
below with reference to these four ammeters, is representative in
nature, and is not intended to be comprehensive.
In FIG. 3, a charging period begins at the moment when both the
switches 304 and 306 are closed, such that the C.sub.T 202 is
connected across the source supply and the ammeter 342 registers
the charging current for C.sub.T 202. An amplitude of a spike in
the charging current is passively limited by the source impedance
of the supply Vs and the parasitic resistance of C.sub.T 202
itself, as well as by the difference between Vs and the voltage on
the C.sub.T 202. The spike amplitude may also be limited by active
control of conduction by the switches 304 and 306. In addition to
controlling peak amplitude, a rate of rise of the charging current,
di/dt, may be limited by limiting the speed with which the switches
304 and 306 are turned on.
At the end of the charging period, the switches 304 and 306 will be
turned off. A change in current will register in the ammeter 342 if
C.sub.T 202 is not fully charged at this time, with a di/dt slope
that depends in part upon the speed with which the series
combination of switches 304 and 306 is turned off. Because the
first clock output 354 and the second clock output 356 are coupled
to corresponding control nodes of switches 304 and 306,
respectively, the outputs 354 and 356 will be driven up to a
voltage greater than their threshold voltages, which will induce a
nonconducting off state in these switches. To drive up the voltage
of the control nodes, these clock outputs source current to drive
the gate capacitance (and/or other parasitic capacitances and
impedances) of the corresponding switch. The drive current will
register in the ammeter 346. Due to the parasitic capacitances, a
high dv/dt gate drive will typically cause a significant capacitive
current spike in the corresponding ammeter 346.
After the switches 304 and 306 are off, a discharge period may
ensue that does not overlap the charge period. To begin the
discharge period, the third clock 362 and the fourth clock 364 will
raise voltages of control nodes of the switches 314 and 312,
respectively, above a Vgs threshold voltage to turn each switch on
to a conducting state. The resulting capacitive gate current of the
switches 312 and 314 will register in the ammeter 346, with a peak
value and di/dt that depend in part upon dv/dt of the clock output.
In order to minimize power dissipation in the switches, the clock
edges in such circuits have typically been made rather fast.
As the later of switches 312 and 314 turns on, C.sub.T 202 begins
discharging into Co 330 with a current that will register in the
ammeter 344. At the end of the discharge clock period, the third
clock output 362 and the fourth clock output 364 sink current to
drive down to an off voltage, causing gate currents, to discharge
the gate capacitance of the corresponding switches, that will
register in ammeter 348. Finally, C.sub.T 202 is disconnected from
Co 330, which may cause another current step to register in the
ammeter 344 if discharging of C.sub.T 202 has not been
completed.
All switches remain off until the clock outputs 354 and 356 sink
current from the gates of switches 304 and 306, respectively, to
reduce the control node voltage of those switches to a level that
is negatively greater than their Vgs thresholds, thereby causing
the switches to turn on and begin the charging period. The sink
current provided by the clock outputs 354 and 356 to effect this
change will register in the ammeter 348. A di/dt of such current
depends substantially upon a magnitude of the dv/dt at which these
clock outputs transition negatively.
Each high di/dt current spike described above is likely to be
coupled into nearby circuitry, whether through mutual inductances,
common impedances, or common connections. Reducing some or all of
the identified noise sources may be desirable for circuits, such as
that described with respect to FIG. 1, which need a charge pump
DC/DC converter but also require very low noise. Various features
of the following figure, taken in combinations, may be employed to
construct such a desirable charge pump. Other benefits will also
become apparent, such as the convenience and simplicity of control
by a single-phase clock.
Quiet Inverting Charge Pump
FIGS. 4, 5 and 6 illustrate an exemplary quiet, inverting
embodiment of a charge pump. FIG. 4 illustrates exemplary circuitry
for establishing current-limited drive circuits (here, inverters),
which may be used within a charge pump clock generating circuit.
FIG. 5 illustrates an exemplary charge pump clock generating
circuit that utilizes current-limited, inverting drive circuits
configured to form a current-starved ring oscillator. FIG. 6
illustrates using a single charge pump clock output to drive all of
the active fly capacitor coupling switches in an exemplary charge
pump. Throughout the descriptions that are set forth below, size
references for some exemplary FET devices are indicated
parenthetically as a channel width (W) and length (L), in micron
units. These size references are appropriate for a low voltage
silicon-on-insulator ("SOI") integrated circuit, and are useful for
relative size considerations. In an exemplary embodiment, threshold
voltages for P-channel MOSFETs are -0.25 V, and for N-channel
MOSFETs are +0.5 V. Device sizes, threshold voltages, and other
considerations may, of course, be adjusted as appropriate for
varying designs and processes, and indeed alternatives to MOSFETS,
such as BJTs or other amplifying/switching devices, may be used
with appropriate adaptation.
FIG. 4 is a schematic diagram of a current limited, inverting drive
circuit. An input voltage supply is connected via Vin+ 402 and
common connection 404. A reference current, limited by a resistor
406, is established through diode-connected MOSFETs 408 (W 7.5, L
2) and 410 (W 7.5, L 4) to create a P-gate reference voltage 412
and an N-gate reference voltage 414. The drive circuit 416 has an
input node 418 and an output node 420, and is formed by connecting
a P-channel FET 422 (W 5, L 0.8) in series with an N-channel FET
424 (W 2, L 0.8), as shown. The drive circuit 416 drives current to
the output node 420, sourcing or sinking current to raise or lower
the voltage of the output node. Circuitry is provided that limits
the current drive capability of the drive circuit 416, as compared
to an absence of such devices. "Absence" of a series device should
be understood to mean replacement by a direct connection, while
"absence" of a parallel device should be understood to mean merely
omission of such device.
The current source capability of the driver circuit 416 is limited
through a source current limit circuit 426, which may, for example,
comprise a P-channel FET 428 (W 1.5, L 2). The FET 428 may be
gate-coupled to the P-gate reference 412 as a current mirror that
limits current, for example, to 1 .mu.A or less. The current sink
capability of the driver circuit 416 may be similarly limited by a
sink current limit circuit 430, comprised for example of an
N-channel FET 432 (W 1.5, L 4) coupled to the N-gate reference 414
as a current mirror (e.g. limited to 1 .mu.A). Establishing 1 .mu.A
current limits in FETs 428 and 432 may require about 5 .mu.A
through reference current FETs 408 and 410, due to the 1:5 size
ratio of the exemplary corresponding devices. Equal magnitudes for
source and sink current limits may reduce undesirable harmonic
generation. Any other appropriate techniques for creating current
limited drive circuits may be employed in the alternative, such as
using low-conductivity FETs or resistors, etc., to restrain either
or both of the source and sink drive capability of such drive
circuit.
Additional circuitry, shown connected by phantom lines to the
P-gate and N-gate references 412 and 414, represents optional
additional current-limited inverter circuits that may be coupled to
the same current reference voltages 412 and 414.
FIG. 5 is a schematic diagram of a ring oscillator 500, which will
be referred to as a "current-starved" ring oscillator operating
with an exemplary period of 1 .mu.S. Inverters 502, 504 and 506 may
be equivalent to the inverter 416 as shown in FIG. 4. Each limits
current from a source supply connection Vin+ 402 by means of a
source current limit 508, 510 and 512, respectively, which may be
equivalent to the source current limit 426 shown in FIG. 4. Each
inverter also limits current from a sink supply connection common
reference 404 by means of a sink current limit 514, 516 or 518,
respectively, each of which may be equivalent to the sink current
limit 430 of FIG. 4. Output transition rates (dv/dt) for the
inverting drive circuit 502 are actively limited by a capacitor 520
(e.g., 90 ff) coupled to its output node, in conjunction with the
"current starving" effect of the source and sink current limits 508
and 514, respectively. Similarly, dv/dt of the output node of the
inverting drive circuit 504 is also actively limited by a capacitor
522 (e.g., 90 ff) coupled thereto, in conjunction with the current
drive limit devices 510 and 516 of the inverting drive circuit
504.
Output transition dv/dt of CLK output 524 of the driver circuit 506
is actively limited by the source and sink current limits 512 and
518, in conjunction with the combined distributed capacitance of
each driven device, which is represented by phantom capacitor 526.
A discrete capacitor may, of course, be added if appropriate. The
devices that constrain dv/dt on the input node of driver circuit
506 also limit dv/dt of the CLK output 524. Series connection of
the three inverting driver circuits 502, 504, and 506, creates a
ring oscillator. The current-starved ring oscillator 500 is an
example of a charge pump clock generating circuit that includes
circuits to reduce switching speeds of substantially all driver
circuits within the clock generator. The current-starved ring
oscillator 500 is also an exemplary circuit for producing a charge
pump clock output 524 for which dv/dt is actively limited in both
negative and positive transitions. Voltage of the CLK output 524
may oscillate substantially rail-to-rail (e.g., between 0 to Vin+)
with low dv/dt transitions, and may have a significantly sine-like
shape.
FIG. 6 is a schematic diagram of a charge pump that may employ a
single phase of a limited dv/dt clock, such as the output CLK 524
of the clock generator 500 shown in FIG. 5. In an exemplary
embodiment, Vin+ is +3V with respect to ground (common reference),
while Vo- is -3V. P-channel MOSFETs 602 and 604 (W 20, L 0.8)
conduct during a charge phase, connecting a fly capacitor 606
(e.g., 10 pf) to the source supply via connections Vin+ 402 and
common reference 404. At a later time, during a discharge period,
the FETs 602 and 604 will be off (nonconducting), and N-channel
FETs 608 (W 20, L 0.8) and 610 (W 5, L 0.8) will conduct,
connecting the fly capacitor 606 between a common reference plus
side, and an intermediate output stored on a storage capacitor
614.
During this discharge period, the N-channel FET 608 couples one
terminal of the fly capacitor 606 to a common reference (404)
connection of the output supply. Concurrently, the N-channel FET
610 couples the opposite terminal of the fly capacitor 606 to the
connection of the output supply (the junction of FET 610 and
capacitor 614) that is opposite to the common reference connection
of the output supply. The area of the device 610 is made much
smaller (e.g., half as large, or less--one fourth as large in the
exemplary embodiment) than the area of the device 608. The smaller
size helps to reduce noise injection into the output, for example
by minimizing coupling of control signals through the gate
capacitance of the FET 610. For a typical FET, the device area is
simply the length times the width. If other processing parameters
are constant, a control node AC impedance (to conducting control
signals into the switch) will vary approximately inversely with
such area. However, control signal AC coupling impedance may be
increased in other ways, for example by reducing the parasitic
gate-body capacitance through increases in the dielectric thickness
or reduction in the dielectric constant. Thus, the device 610 may
be configured in various ways to have at least twice the control
node AC impedance of the device 608.
The voltage on storage capacitor 614 is filtered, by means of a
resistor 616 and filter capacitor 618, to provide a filtered output
supply voltage Vo- with respect to common reference 404. The
exemplary embodiment provides a quiet output but relatively low
current capacity. The skilled person will readily adjust the
current capacity of a circuit such as that of FIG. 6, for example
by employing small (to zero) values for the resistor 616, or by
replacing resistor 616 with a primarily inductive impedance. Larger
devices may also be employed for any or all of FETs 602, 604, 608
and 610, as well as a larger fly capacitor 606.
Each of the FETs 602, 604, 608 and 610 is an example of an actively
controllable transfer capacitor coupling switch ("TCCS"). First,
each is disposed in series to couple a node of the transfer
capacitor to the source supply (for charging switches) or to the
output supply (for discharging switches). Second, the conductivity
of each is actively controllable, under control of a signal applied
to a control node of the switch (here, the gate of the FET). Such a
control node has a significant impedance to primary conducting
connections (here, the source and drain connections).
As shown in FIG. 6, the gate (control node) of each TCCS 602, 604,
608 and 610 may be capacitively coupled to the appropriate clock
signal by means of a corresponding coupling capacitor in
conjunction with a bias resistor. Direct coupling could be employed
by use of appropriate level shifting and isolation considerations.
For the FETs 602, 604 and 608, capacitive coupling is effected by
means of capacitors (e.g., 1 pf) 618, 620 and 622, respectively,
together with resistors (e.g., 10 M.OMEGA.) 626, 628 and 630,
respectively.
In the case of a FET 610, the coupling is effected by two coupling
circuits connected in series to reduce voltage stresses. Thus, a
capacitor 636 (e.g., 2 pf) couples the CLK 524 to an intermediate
node where it is biased by a resistor 638 (e.g., 10 M.OMEGA.) to an
intermediate average voltage level (common reference voltage, in
this case). From this intermediate node the charge pump clock
output signal is coupled via a capacitor 624 (e.g., 2 pf) to the
gate of the FET 610, and biased by a resistor 632 (e.g., 10
M.OMEGA.) to the source voltage of the FET. The modified capacitive
coupling circuit for the FET 610 provides an example of a modified
circuit that differs in some regard, but functions substantially
equivalently, to another. Any circuit illustrated or described
herein may be replaced (as needed) by such a modified circuit, if
substantially the same function is performed. Extended voltage
capacity circuits, such as series or cascode-coupled transistors or
the series capacitors described above, and increased current
capacity circuits, such as parallel combinations of transistors,
are examples of such equivalent circuits that may be employed, in
place of any illustrated circuit, to satisfy particular design
goals.
In the exemplary circuit, N-channel switches such as FETs 608 and
610 are switched on concurrently while P-channel switches such as
FETs 602 and 604 are off, and the converse is also true. The gate
threshold voltage of N-channel switches is positive (e.g.,
conductive for Vgs>0.5V), while the gate threshold voltage of
P-channel switches is negative (e.g., conductive for
Vgs<-0.25V). The active limitation of the dv/dt of transitions
of CLK 524 therefore creates a period of time when all switches are
off (i.e., the duration of the transition from [average of CLK 524
-0.25] to [average of CLK 524 +0.5V]. Single-phase clock drive of a
charge pump may be effected using different types of switches that
have correspondingly different control voltage thresholds. However,
bias voltages may need to be adjusted accordingly to avoid
simultaneous conduction of devices, such as FETs 602 and 608, that
are disposed in series across a supply. The circuits and devices of
FIG. 6 provide a convenient approach for driving all actively
controllable TCCSs of a charge pump from a single clock phase
(e.g., CLK 524), while ensuring that conduction periods for series
fly capacitor coupling switches do not inadvertently overlap.
Each capacitive gate drive circuit shown in FIG. 6 has a time
constant .tau. which may be expressed in terms of drive periods as
R*C/(clock drive period). In the exemplary circuit of FIG. 6, .tau.
is approximately 10 periods, because the switch drive signal CLK
524 has a period of about 1 .mu.S. However, in many circumstances
.tau. may be varied widely without unduly affecting operation of
the circuit. .tau. may be enlarged as much as desired, though this
may adversely affect device area. In some circumstances, .tau. may
also be reduced, and allowed to range for example down to 5
periods, to 2 periods, to 1 period, or even to 0.1 period or less
without unduly impairing performance. Such reduction of .tau. may
reduce the amplitude of the gate drive applied to the corresponding
MOSFET, particularly if it is accomplished by reducing the size of
the coupling capacitor (e.g., 618, 620, 622 or 624). This is due in
part to capacitive voltage division between the coupling capacitor
and the MOSFET gate capacitance. Such voltage division may reduce
the magnitude of the control node voltage (Vgs), and hence may
reduce conductivity of the switches when they are nominally
enabled. Reducing .tau. may also reduce the proportion of time
within each cycle during which the corresponding switch is turned
on, which may in turn increase ripple voltages and/or load current
capacity. The wide range from which .tau. may otherwise be chosen
may be limited by such engineering considerations.
Alternative Charge Pump Embodiments
Charge pumps are extremely versatile, and aspects of the charge
pump method and apparatus herein may be employed in virtually any
charge pump configuration. Some alternative techniques are set
forth below, each of which may be implemented using aspects of the
method and apparatus described herein.
FIG. 7 is a schematic diagram of a charge pump that generates a
negative voltage Vo- 710, and provides an example of using passive
transfer capacitor coupling switches. A clock source CLK 524 is
provided, which may be generated, for example, by the circuit of
FIG. 5. A transfer capacitor 702 charges via the clock source and
via a passive switch 704 when CLK 524 is at a maximum value. When
CLK 524 is at a minimum value, the transfer capacitor 702
discharges via the clock sink and a passive switch 706.
Passive switch 704 may be an N-channel enhancement MOSFET connected
drain to gate and having a low threshold voltage of about 0.5V, or
may be a diode (anode to capacitor 702, cathode to ground), for
example a low-voltage Schottky diode. Passive switch 706 may
similarly be a diode-connected N-channel enhancement FET, or may be
a discrete diode with anode to output capacitor 708, cathode to
transfer capacitor 702. The dv/dt control of the drive CLK 524
effects quiet operation. However, there is some loss of efficiency
and voltage output due to the non-zero forward conduction voltage
of the devices 704 and 706. Thus, if CLK 524 is 3V p-p (e.g.,
oscillates between +3V and common), then Vo- 710 may be only about
-2.5V, even at light loads.
Passive switches similar to devices 704 or 706 may be substituted
in place of one or more active switches in many designs described
herein, simplifying design but typically reducing output voltage.
For example, in FIG. 6, either or both of the active switches 604
and 610, together with their associated drive coupling circuitry,
may be replaced by passive devices similar to devices 704 or 706.
Passive switches are controlled by a charge pump clock output, but
not via a control node. Rather, connections to primary conduction
nodes of such switches are driven, through circuit operation
controlled by a charge pump clock output, to voltage levels at
which the devices passively switch on or off.
FIG. 8 is a schematic diagram of an active p-switch 800 and of an
active n-switch 830. Each is driven by a clock CLK 802. The
p-switch 800, when "on," connects an external supply (e.g., V+ 804)
to a fly capacitor for a charge pump, represented by Cp 806. The
n-switch 830, when "on," connects a charge pump fly capacitor (or
transfer capacitor), represented by Cp 814, to a supply connection
such as V- 816. The p-switch 800 couples CLK 802 to the gate of a
P-channel MOSFET 808 via a coupling capacitor 812 and a bias
resistor 810. With the bias resistor 810 connected to the source of
the FET 808, it is preferable that the FET 808 has a small negative
threshold voltage (e.g., -0.25V). For the n-switch 830, the gate of
an N-channel MOSFET 818 is coupled to CLK 802 via a coupling
capacitor 822, with a bias resistor 820 setting the average Vgs to
zero volts. In this circumstance, it is preferred that the
threshold voltage for the FET 818 has a small positive value (e.g.
0.5V). Depending upon voltage levels, these switches 800 and 830
may employ series capacitive coupling circuits, and/or cascode or
other extended-capability circuit equivalents. The effective .tau.
of each capacitive coupling circuit may be set in accordance with
the operating frequency of a charge pump in which it is used,
ranging from 10 clock periods or more down to 0.1 clock periods or
less, as described with respect to FIG. 6. The .tau. of the
capacitive coupling circuit within each n-switch and p-switch
operating within a single charge pump under control of the same
clock (e.g., CLK 524) may have substantially the same value.
P-switches 800 and n-switches 830 may have different thresholds
while operating from a common clock signal, provided that the bias
voltage is set properly to ensure that a p-switch and an n-switch
connected in series across a supply are precluded from concurrent
conduction.
FIG. 9 is a block schematic diagram that illustrates "stacking"
charge pump circuits to obtain higher or lower output voltages.
Each switch 800 and 830 may be as illustrated in FIG. 8, or as
discussed in the text describing FIG. 8. The circuit of FIG. 9 may
be configured as either a voltage tripler, or a voltage quadrupler,
as follows: Va 904 may be connected to a positive source voltage
Vs+, and Vb 906 may be connected to a common reference voltage
(ground). Vc 908 may also be coupled to Vs+. Operation of the
n-switches and the p-switches connected to a transfer capacitor 902
will cause Vd 910 to be driven to 2*Vs+. Ve 914 may be connected to
Vd 910, and Vf 916 may be connected to ground. With those
connections, an output voltage Vh 920 will be driven to
approximately 3*Vs+ by means of fly capacitor 912 if Vg 918 is
connected to Vs+. However, the output voltage Vh 920 will be driven
to approximately 4*Vs+ if Vg 918 is connected, instead, to Vd 910.
A storage capacitor, though not shown, is generally provided
somewhere to store and smooth each of the voltages Va 904, Vc 908,
Vd 910, Ve 914, Vg 918 and Vh 920.
The circuit of FIG. 9 may also be configured to produce negative
voltages. Vh 920 may be connected to a positive source voltage Vs+,
while Vg 918 and Ve 914 are connected to a reference (ground)
voltage, to produce -(Vs+) at Vf 916. Vc 908 and Va 904 may be
connected to Vf 916. An output Vb 906 will be approximately -2*Vs+
if Vd 910 is connected to ground. If, instead, Vd 910 is connected
to Vs+, then output Vb 906 will be driven to approximately -3*Vs+.
Capacitive storage, not shown, is assumed for each supply and
intermediate voltage.
In FIG. 9, all of the p-switches 800 and all of the n-switches 830
may be controlled by a single phase of a clock, such as CLK 524 of
FIG. 5. Alternatively, a single phase of a first clock may control
the switches connected to the fly capacitor 912 (i.e., the switches
of a charge pump section 922), while a single phase of a different
second clock may control the switches connected to the fly
capacitor 902 (i.e., the switches of a charge pump section 924). If
the clocks for charge pump sections 922 and 924 are inverted from
one another, then the charge pump sections may be disposed in
parallel to create a push-pull charge pump. That is, Va 904 may be
connected to Ve 914, Vb 906 to Vf 916, Vc 908 to Vg 918, and Vd 910
to Vh 920. Such a push-pull charge pump may, for example, provide
lower ripple voltage and higher output current capabilities.
Additionally, in circuits otherwise comporting with FIG. 9, one or
more passive switches (such as switches 704 or 706 in FIG. 7) may
replace switches in FIG. 9 that are shown (in FIG. 8) to be
controlled by a charge pump clock output signal coupled to a
control node of the switch. For example, the p-switch connected to
Vg 918 and/or the n-switch connected to Vf 916 may be replaced by a
passive switch, or by a diode. Similar substitutions may be made
for the switches connected to Vc 908 and/or to Vb 906.
Moreover, if Vd 910 and Va 904 are equivalent to Vin+ 402 and
common reference 404 of FIG. 5, then the left side of the transfer
capacitor 902 may be coupled directly to a charge pump clock output
such as 524, which would omit the left-side switches of the pump
section 924 in FIG. 9. The left-side switches of section 922 of
FIG. 9 may be omitted under analogous circumstances, with the left
side of the transfer capacitor 912 coupled directly to a charge
pump clock output instead. In such a configuration, transfer
capacitor charging current and discharging current may be limited
not only by a drive signal (such as that on capacitor 522 in FIG.
5) that has a limited dv/dt, but further or alternately by a
current limiting device such as 512 or 518.
FIG. 10 is a simplified schematic diagram that illustrates
generation of arbitrary voltages by means of charge pump
techniques. A source voltage Vs+ 1002 may be used to derive an
intermediate voltage, for example by means of resistors 1004 and
1006. Such intermediate voltage may optionally be buffered, if
significant current output is desired, by means of buffer amplifier
1008, or may at least be connected to ground via a decoupling
capacitor (not shown), to produce a projection voltage 1010 (with
respect to common, or ground). The projection voltage 1010 may be
regulated, for example by means of feedback (not shown) applied to
amplifier 1008. P-switches 800 and n-switches 830 may be employed
in conjunction with a fly capacitor 1012, as shown. Vb may be an
available voltage source (e.g., Vs+). Operation of the circuit will
establish Va 1014 at a voltage approximately equal to that of Vb
1016 plus the projection voltage 1010. The skilled person will
readily see that rearrangement of the circuit will permit
generation of arbitrary negative voltages with equal simplicity.
Larger voltages may be obtained by stacking charge pump circuits,
in a manner as described with respect to FIG. 9. Thus, arbitrary
positive or negative voltages may be generated by means of charge
pump circuits. All such charge pump circuits may be controlled by a
single phase of a clock. Of course, the switches associated with
different fly capacitors may alternatively use different clocks for
control. Active switches may also be replaced with passive
switches, for example in a manner as described with respect to FIG.
7 or FIG. 9.
Innumerable alternative embodiments of the charge pumps described
above are possible. Any clock generator may be employed. It is
desirable that the clock generator avoid introducing high di/dt
noise on the supply, as can be achieved with many analog designs
(for example, as shown in FIG. 5) and some digital designs. It is
desirable that dv/dt of the clock drive signals be limited, both to
help limit control node signal injection, and also to help limit
(in conjunction with the transconductance of the relevant switch)
the resulting di/dt of charging and discharging currents. It may be
desirable to capacitively couple a charge pump clock to a control
node of a transfer capacitor switch, for example in order to
simplify control of control-node voltage levels. It may be
desirable to utilize a single-phase clock output to control many,
or all, of the transfer capacitor active switches within a charge
pump, to minimize circuit complexity. Any of these desirable
features may be effected independently, or in combination with any
of the other desirable features, or in combination with any other
feature described herein. Thus, the skilled person may apply
aspects of the method and apparatus described herein to a
staggering variety of charge pump configurations.
CONCLUSION
The foregoing description illustrates exemplary implementations,
and novel features, of aspects of a charge pump method and
apparatus for generating new voltages in circuits. The skilled
person will understand that various omissions, substitutions, and
changes in the form and details of the methods and apparatus
illustrated may be made without departing from the scope of the
invention. Numerous alternative implementations have been
described, but it is impractical to list all embodiments
explicitly. As such, each practical combination of apparatus and
method alternatives that are set forth above or shown in the
attached figures, and each practical combination of equivalents of
such apparatus and method alternatives, constitutes a distinct
alternative embodiment of the subject apparatus or methods. For
example, a charge pump having a plural transfer capacitor (or
`stacked`) architecture as shown in FIG. 9, having at least one
passive switch as shown in FIG. 7, and having a settable voltage
source as shown in FIG. 10, constitutes an embodiment of the
subject apparatus, as do all other such practical combinations of
subfeatures. Therefore, the scope of the presented invention should
be determined only by reference to the appended claims, and is not
to be limited by features illustrated in the foregoing description
except insofar as such limitation is recited in an appended
claim.
All variations coming within the meaning and range of equivalency
of the various claim elements are embraced within the scope of the
corresponding claim. Each claim set forth below is intended to
encompass any system or method that differs only insubstantially
from the literal language of such claim, as long as such system or
method is not, in fact, an embodiment of the prior art. To this
end, each described element in each claim should be construed as
broadly as possible, and moreover should be understood to encompass
any equivalent to such element insofar as possible without also
encompassing the prior art.
* * * * *